Certain government standards exist for regulating fuel tanks for use in various vehicles, such as armored vehicles, tanks, and race cars; aircraft such as helicopters, commercial and private aircraft, tactile missiles, and other aerospace vehicles; marine craft; and other vehicles. Fuel tanks must be able to withstand certain crash parameters, such that they limit rupturing of the tank and the consequent dangers associated therewith. Accordingly, fuel tanks for use in the aviation field, particularly for crash worthy helicopters applications, are often made of two pieces: a rigid outer tank and a flexible inner tank.
The rigid outer tank generally provides a constant, predictable shape that facilitates attachment of the fuel tank to other components of the aircraft, such as for installation of the tank into the fuselage, wings, bays, or other available space of the aircraft. For example, some known rigid outer tanks are made of a composite material featuring a fiber-reinforced epoxy or other thermosetting resin. While thermosetting composite materials are generally considered to provide favorable characteristics for the rigid tank, they often have limited elongation before breaking (e.g., usually less than 10% elongation) and do not absorb a sufficient amount of energy without other components to meet government crash standards.
Accordingly, the flexible inner tank is typically installed inside the rigid tank to make the overall tank assembly more crash resistant. For example, the flexible inner tank is often made with a rubber reinforced with polyamide fabric (or polyester fabric) or some other construction that will distort to absorb energy in the event of a crash. In some cases, the thickness of the flexible inner tank is increased to provide greater crash resistance. However, the addition of the flexible inner tank (or the addition of material thereto to attain a greater thickness) adds weight to the system, which is undesirable in many instances.